a. Field of the Invention
The present invention concerns in-band signaling in a voice communications network and, in particular, concerns handshaking between customer premises equipment (CPE) and a switching system to facilitate the communication of in-band data, such as caller identity information for example.
b. Related Art
.sctn. 1.1 Caller ID
Many regional bell operating companies ("RBOCs") and other telephone service providers (collectively referred to as "TELCOs") have provided enhanced telephone services. One such enhanced service is Calling Number Delivery ("CND"). Basically, when a customer having Calling Number Delivery service and compatible equipment receives signals (e.g., ringing patterns) indicating an incoming call, the TELCO will transmit data which identifies the party calling between the ringing pattern signals. While the customer's equipment is on-hook, the information regarding the identity of the calling party is provided (e.g., via LCD display) to the customer. Thus, the customer can decide whether or not to answer the call based on the identity of the calling party. The physical layer, data link layer, and message assembly layer requirements of the Calling Number Delivery data are known to those skilled in the art and described in the Bellcore Generic Requirements entitled, LSSGR: Voiceband Data Transmission Interface Section 6.6, GR-30-CORE, Issue 1 (December 1994) (hereinafter referred to as "GR-30-CORE" and incorporated herein by reference). In general, if the customer's line goes off-hook during data transmission, the data transmission is pre-empted or stopped and normal call completion treatment is executed.
.sctn.1.1.1 CID On-Hook Data Transmission Protocol
As discussed briefly above, when a CID compliant CPE is on-hook, data identifying the caller is transmitted between the first and second power ringing patterns. For example, as shown in the known method of FIG. 1A, data may be transmitted during a time 104 starting 0.5 to 1.5 seconds (t.sub.1) after a first ringing pattern 102 and ending at least 200 ms (t.sub.2) before a second ringing pattern 106. If power ringing patterns are not provided, the data may be transmitted after an Open Switching Interval ("OSI") and a silent interval. For example, as shown in the known method of FIG. 1B, a time period for data transmission 154 follows a 150 to 350 ms OSI 152, and a 300 ms silent period t.sub.3. In general, if the line goes off-hook during data transmission, the data transmission is pre-empted or stopped and normal call completion treatment is executed.
.sctn.1.2 Caller Identity Delivery on Call Waiting
.sctn.1.2.1 Purpose of CIDCW
Most TELCOs offer enhanced caller ID services such as Calling Identity Delivery on Call Waiting ("CIDCW") for example. If a customer has Calling Identity Delivery on Call Waiting service and compatible equipment, when they are off-hook and connected with a second party ("the far-end party") and a third party ("the waited party") calls the customer, following a handshaking protocol, the customer is alerted to the fact that the third party is waiting and is provided (e.g., via LCD display) with information regarding the identity of the waiting third party. Thus, the customer may chose to ignore the waited third party, or put the far-end second party on hold and establish a connection with the waited third party, etc. based on the provided identity information.
.sctn.1.2.2 Devices for Facilitating CIDCW
As mentioned above, TELCOs offer different services to their customers. However, to use such services or to fully exploit such services, the customers need compliant equipment at their premises. Although different types and classes of customer premises equipment ("CPE") are known to those skilled in the art and described in the Bellcore Special Report entitled, Classes of Customer Premises Equipment, SR-INS-002726, Issue 1 (August 1993) (hereinafter referred to as "SR-INS-002726" and incorporated herein by reference), relevant classes of Customer Premises Equipment will be described below for the reader's convenience.
Type 1 Customer Premises Equipment can receive and interpret on-hook data transmissions which use the single data message format ("SDMF") and the multiple data message format ("MDMF") and supports Calling Number Delivery, Calling Name Delivery, and Visual Message Waiting Indicator services. (SDMF and MDMF are defined in GR-30-CORE.) In addition to supporting the services supported by Type 1 CPE, Type 2 Customer Premises Equipment can receive and interpret off-hook data transmissions which use the multiple data message format ("MDMF"). Thus, Type 2 CPE can further support Calling Identity Delivery on Call Waiting services. Finally, in addition to supported the services supported by Type 1 and Type 2 CPE, Type 3 CPE conform with the Analog Display Service Interface ("ADSI") and protocol and further supports ADSI Server Display Control and Feature Download services, as well as ADSI-based Visual Features services such as Visual Screening List Editing, Call Waiting Deluxe, and Visual access to information services such as directory, home banking, etc.
.sctn.1.2.3 Basic Operation of CIDCW
As discussed above, both Type 2 and Type 3 CPEs support Caller Identity Delivery on Call Waiting (CIDCW) service. Although the data transmission protocol for the CIDCW service is known to those skilled in the art and described in GR-30-CORE, a high level description of the data transmission protocol is provided below for the reader's convenience.
As discussed above, customers having CID (or CIDCW) service and compatible equipment can receive information identifying a waited party while that customer is off-hook. For example, as shown in FIG. 2, a third party (waited party) 212 may call an off-hook first party (CIDCW customer) 204 having an established connection 206, 220, 208, via a central office switch 202, with a second party (far-end party) 210. The central office switch 202 (e.g., a stored program controlled switching system or "SPCS") should alert the CIDCW customer 204 that a call is waiting and should inform the CIDCW customer 204 of the identity of the waited party 212. Although the process for alerting and informing the CIDCW customer 204 is known to those skilled in the art and described in GR-30-Core, it is explained below with reference to FIGS. 3, 4A, and 4B for the reader's convenience.
FIGS. 4A and 4B are timing diagrams which represent signaling from a central office switch 202 (e.g., an SPCS) to a CIDCW party 204. FIG. 3 illustrates the CAS-ACK handshake and call waiting data transmission between the central office switch 202 and the CIDCW party 204. The timing diagrams are not necessarily to scale.
FIG. 4A is a timing diagram of a successful attempt by the central office switch to transmit caller identification data to the CIDCW party 204. First, as shown in time period 402, the central office switch 202 may create an open switching interval (OSI) during which the DC voltage between the tip and ring of a line is removed, thereby temporarily suspending line supervision and transmission. This time period 402 is optional and preferably lasts between 0 and 300 ms. Next, as shown in time period 404, the central office switch 202 mutes the far end party 210 before generating an alerting sequence on the line. Next, as shown in time period 406 and in FIG. 3, the central office switch 202 places a subscriber alerting signal ("TSAS") onto the line. The SAS is an audible signal which alerts the CIDCW party 204 that a caller is waiting. The SAS preferably occurs within a 250 ms to 1 second window 406. After a transition time 408 of, for example, 0 to 50 ms, the central office switch 202 provides a CPE alerting signal (CAS) to the CIDCW party 204, as shown in time period 410 and FIG. 3. The time window 410 is preferably between 80 and 85 ms.
During an acknowledgment time-out period 412, the central office switch 202 waits for an acknowledgment signal (ACK) from the CIDCW party 204. The time-out period 412 is preferably between 155 ms and 165 ms. The timing diagram of FIG. 4A illustrates the time periods following the receipt of an acknowledgment signal from the CIDCW party 204 during the time-out period 412 (i.e., a successful handshake). After an optional transition period 414 of, for example, 50 ms to 500 ms, the central office provides the caller identity data (encoded in frequency shift keying ("FSK")) to the CIDCW party 204 during time period 416. After an optional OSI time period 418 and an optional delay to voice path period 420, the voice path between the CIDCW party 204 and the far-end party 210 is restored. That is, the central office switch 202 un-mutes the far-end party. As shown in the timing diagram of FIG. 4B if an acknowledgment signal from the CIDCW party 204 is not received during the time-out period 412 (i.e., an unsuccessful handshake), then, after an optional OSI time period 418 and an optional delay to voice path period 420, the voice path between the CIDCW party 204 and the far-end party 210 is restored.
.sctn.1.3 Problems and/or Constraints with CIDCW
Problems may arise when, as shown in FIG. 5, multiple extensions (referred to as pieces of customer premises equipment or "CPEs") 502 share a CIDCW party's 204 line 206. More specifically, caller identity data, encoded as FSK data, is "in-band" data. That is, the FSK data is within the voice band of the connection 206, 220, 208. If a single Type 2 or Type 3 CPE is provided on the line 206, then the CPE will mute its transmit (talk) and receive (listen) paths so that the user of the CPE does not hear annoying FSK in-band data transmissions and so that the speech of the user of the CPE does not interface with FSK detection. However, if the line 206 is provided with more than one CPE 502, then the CAS-ACK handshake and the FSK data transmission becomes much more complicated.
If a Type 1 CPE is off-hook when a CAS is received, an acknowledgment signal ACK is not sent because Type 1 CPEs are not intelligent enough to mute their transmit and receive paths in response to a CAS. Moreover, if more than one Type 2 or Type 3 CPEs are concurrently off-hook when a CAS is received, only one of the CPEs should provide an acknowledgment ACK signal. Otherwise, the multiple acknowledgment signals ACK may distort the acknowledgment handshake to such an extent that detection of the acknowledgment signal ACK by the central office switch 202 is precluded. In such instances, the central office switch 202 will not provide the caller identity data. Finally, Type 2 and Type 3 CPEs transmit different acknowledgment signals ACK in response to a detected CAS. Since the functionality of Type 3 CPEs supersedes that of Type 2 CPEs, if both a Type 2 and a Type 3 CPE are concurrently off-hook when a CAS is received, only the Type 3 CPE should respond with an acknowledgment signal ACK.
.sctn.1.4 Flash Signals
After a successful CAS-ACK handshake and an FSK caller identity data transmission, the voice path is reestablished as described above with reference to FIG. 4A. A CPE 502 may provide a flash signal (i.e., an on-hook line condition for a predetermined period of time) to the central office switch 202 to activate a feature specific option. Basically, a flash signal causes the central office switch 202 to place the current far end party 210 on hold and connects the waited party 212 to the CIDCW party 204. A subsequent flash signal causes the central office switch 202 to connect the held party 210 to the CIDCW party 204 and to place the originally waited party 212 on hold.
.sctn.1.4.1 Constraints with Flash Signaling
When a line 206 is provided with multiple CPEs 502, all off-hook CPEs, except one, must return to the on-hook condition so that the one CPE can generate a flash hook signal on the line.
.sctn.1.5 Related Patents and Their Problems and/or Limitations
U.S. Pat. No. 5,263,084 ("the Chaput et al patent") discusses a CIDCW system in which an acknowledgment signal is not provided if any extensions of a CIDCW party are off-hook. However, the Chaput et al patent does not describe a system which considers whether the CIDCW compliant CPEs are of different types (e.g., Type 2 and Type 3) and does not specify how an off-hook condition is determined. Moreover, the system discussed in the Chaput et al patent apparently will not provide an acknowledgment signal if any extension is off-hook. Furthermore, the Chaput et al patent does not address and describe flash signaling when multiple extensions are off-hook.
U.S. Pat. No. 5,583,924 ("the Lewis patent") discusses a system in which multiple conforming CPEs ("CCPEs") (e.g., Type 2 or Type 3 CPEs) share a single line. In response to a CAS signal, each of the CCPEs goes on-hook. A primary CPE then goes off-hook and transmits an acknowledgment signal to the central office. After the caller identity data is received by the CCPEs, the CCPEs go off-hook, the primary CCPE goes on hook, and all CCPEs display the caller identity information. If any non-conforming CPEs ("NCPEs") (e.g., Type 1 CPEs) are off-hook, the primary CCPE does not go off-hook to transmit the acknowledgment signal. Unfortunately, in the system discussed in the Lewis patent, the primary CCPE is apparently predetermined. Thus, any added CCPEs may not be designated as a primary CCPE. Furthermore, if the primary CCPE fails, the system will not work. Finally, the system discussed in the Lewis patent apparently does not distinguish between different types of CCPEs (e.g., Type 2, Type 3, etc.).